net: Allow netdevices to specify needed head/tailroom

This patch adds needed_headroom/needed_tailroom members to struct
net_device and updates many places that allocate sbks to use them. Not
all of them can be converted though, and I'm sure I missed some (I
mostly grepped for LL_RESERVED_SPACE)

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/econet/af_econet.c b/net/econet/af_econet.c
index 68d1544..7c9bb13 100644
--- a/net/econet/af_econet.c
+++ b/net/econet/af_econet.c
@@ -340,7 +340,7 @@
 
 		dev_hold(dev);
 
-		skb = sock_alloc_send_skb(sk, len+LL_RESERVED_SPACE(dev),
+		skb = sock_alloc_send_skb(sk, len+LL_ALLOCATED_SPACE(dev),
 					  msg->msg_flags & MSG_DONTWAIT, &err);
 		if (skb==NULL)
 			goto out_unlock;